Apparatus and method for combustion

ABSTRACT

To enable a burnpot for a corn burning stove to be continuously operated, the burnpot has either: (1) an openable bottom with at least a first and second position, one of the at least first and second positions being substantially closed to enable a body of combustible fuel to burn on its upper surface, the other of the at least first and second positions providing an opening, burnpot side wall portions and a top of the burnpot being shaped so as to permit a solid clinker to drop out of the opening in the openable bottom when the openable bottom is in its second position; or (2) a bottom formed as one of a series of sections of a rotatable member so that as the member rotates, it carries ash with it away from the bottom of the burnpot. A combustion volume is provided between the openable bottom or rotatable bottom, the side surfaces and the top, the combustion volume having an upper portion and a lower portion whereby a fire on a combustion surface in the lower portion burns upwardly toward the upper portion so that byproducts of combustion build on the combustion surface to cause burning fuel to burn at a higher level; the higher level having a smaller cross sectional area than the lower portion whereby the byproducts of combustion may drop as a unit out of the burnpot bottom opening. Easy to ignite fuel is moved from one hopper into the burnpot and ignited. When the temperature is high enough to ignite the harder to ignite fuel it is moved into the burnpot and the flow of easy to ignite fuel stopped.

RELATED CASES

This application is a continuation-in-part of U.S. patent application Ser. No. 10/410,118 filed Apr. 9, 2003, and this application is a continuation-in-part of provisional patent application 60/779,750 filed Mar. 7, 2006, both in the name of Terry L. Krumrei. Applicant claims the benefit of the filing date of provisional patent application 60/779,750 filed Mar. 7, 2006.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatuses for combustion and more particularly to a combustion technique and equipment including a burnpot system, a fuel hopper and a method of operating the burnpot system and fuel hopper.

It is known to provide a combustion system for removing ash conveniently from the bottom of a burnpot with moving walls. The prior art moving walls slide open or swing open, either completely open such as by sliding out of the bottom or partly open such as in the case of moveable grates that move back and forth to open and close. The ash drops out of the burnpot and is removed either manually or mechanically. The prior art systems of this type are difficult to operate automatically for long periods of time.

It is also known to provide automatic means for igniting fuel fed to a burnpot to start the fire. These systems utilize an electric heater to superheat air and use the superheated air to ignite the fuel in the burnpot. This approach works well with some fuels such as wood pellets but not for others such as corn or other unconventional biomass fuels which have higher ignition temperatures.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a novel burner, such as for example a stove or furnace.

It is a further object of the invention to provide a novel method for providing heat by combustion.

It is a still further object of the invention to provide a novel burnpot for use in a burner.

It is a still further object of the invention to provide a burnpot technique which is designed for the automatic removal of ash from a stove or burner.

It is a still further object of the invention to provide a novel ignition system for ignition of difficult to ignite fuels.

In accordance with the above and further objects of the invention, a novel burnpot has an ash removing section that includes a movable bottom with the ability to remove ash as needed. For this purpose, the bottom of the burnpot includes a rotatable portion having a substantially horizontal axis of rotation and cylindrical side rims perpendicular to the axis of rotation. The rotatable portion includes a portion of a closed surface substantially parallel to the axis of rotation. In the preferred embodiment, the closed surface is shaped substantially as a right regular cylinder or drum but may have other shapes such as a right regular prism having a plurality of faces. Preferably, there are also a plurality of dividing surfaces parallel to the axis of rotation extending radially outwardly from the faces of the cylinder to the bottom of the stationary side walls of the burnpot and extending to the same height as the side rims to divide the closed surface into a plurality of sections each of which is bounded by a portion of the face of the cylinder, portions of the side rims and the dividing surfaces. These sections form a plurality of different movable closed bottom sections of the firepot. Together they can close the bottom of the burnpot at different rotary positions of the cylinder. With this mechanism, the burnpot always has a bottom in place that can hold ash and combustible fuel and the combustible fuel can burn at least on the upper surface of the cylinder.

In one embodiment, the surface of the cylinder is divided into four sections of 90 degrees each. In another embodiment, it is divided into three sections. The newly added fuel is ignited and burns on the top surface of the section closing the burnpot bottom for a period of time short enough to avoid excessive concentration of heat and high temperatures. Because the top fuel burns first, the temperature of the surface of the cylinder is not heated excessively. The cylinder may be rotated before the newly added fuel has been thoroughly burned. The number of sections on the drum and the rate of rotation may be selected for the fuel that is to be burned. It is also possible to control the air flow. These options are selected to avoid excessive heat that may cause some fuels to develop clinkers that attach too strongly to the drum or walls of the burnpot. Scrapers and/or cutting members may be incorporated to remove ash from the drum after it has rotated beyond the bottom of the burnpot. Ash containing unburned fuel may be recirculated if desired.

The side walls perpendicular to the axis of rotation may be of different construction. In one embodiment, there are cylindrical side walls perpendicular to the closed surface and the axis of rotation at the ends of the drum or cylinder and radially-extending dividing walls perpendicular to the closed surface and parallel to the axis of rotation. The dividing walls in the preferred embodiment are formed of rows of pins that can be attached at different locations on the cylinder or drum. Cutting members move between the pins to fragment clinkers. In other embodiments, the dividing walls are solid and scrapers scrape the drum to remove the products of combustion. The closed surface and the walls may have openings for air or may be solid.

With this approach, the area and time of burning are spread. The metal surface of the cylinder does not rise to as high a temperature because the burning is spaced from the bottom by fuel that is not yet ignited before the cylinder is rotated and after the cylinder is rotated, the fuel is not pressed against the bottom of the cylinder by gravity but instead is repositioned. The lower concentration of heat avoids binding of the fuel with the surface of the cylinder and reduces melting of the fuel to form large clinkers. Further rotation of the cylinder causes the ash to drop from the ash removing section of the burnpot. A mounting structure is positioned with respect to the cylinder so that the cylindrical surface always closes the burnpot at the bottom end of the burnpot. The cylinder extends sufficiently beyond the opening at the lower end of the burnpot to carry the products of combustion out of the burnpot when the rotatable cylinder is rotated.

The rotatable bottom has a radius of curvature sufficiently large to provide a bottom to the burnpot that avoids excessive collection of the combustible fuel at the outer edges of the burnpot bottom. More specifically, the radius of curvature of the rotatable bottom is sufficiently large with respect to the size of the burnpot bottom opening so that the distance between the lowest point on the burnpot bottom is no more than 24 inches from the highest point. The burnpot side wall portions and top are shaped to permit a solid clinker to move out of the burnpot bottom opening by rotation of the rotatable cylinder. For this purpose, there are spring biased movable members and scraping rods. The spring biased movable members are positioned to hold the combustible fuel and ash on the rotatable cylinder as the fuel and ash are rotated to a side position and the scraper removes the ash and clinkers near the lower portion of the rotation of the drum. Preferably the members are permeable to permit aeration and the dropping free of fine ash. They are spring biased against the cylinder so that large clinkers can force the members outwardly and drop from the cylinder.

A fuel feed and ignition system includes at least first and second fuel hoppers and fuel moving apparatus in contact with at least first and second fuel hoppers. A control system moves from fuel feed setting to fuel feed setting in a controlled serial sequence with a delay time between settings to avoid a rapid change in rates of fuel feed. The fuel moving apparatus is positioned to move the fuel from either the first or the second fuel hoppers into the burnpot. The control system includes a switching system having at least a first state and a second state. The switching system energizes the fuel feed system to move fuel from the first hopper into the burnpot and energizes an ignition system when in the first state. When the switching system is in the second state, it energizes the fuel feed system to move fuel from the second hopper into the burnpot. The switching system switches from the first state to the second state when the temperature in the burnpot reaches the ignition temperature of the fuel in the second hopper. In operation, easily ignitable fuel is fed into a burnpot from a first hopper and ignited. A harder to ignite fuel is fed into the burnpot when the temperature in the burnpot is above the ignition temperature of the harder to ignite fuel.

In another embodiment, the burnpot bottom is either a rotatable cylinder or a slide. The bottom is combined with a different feed and ignition system. In this embodiment, a slide is positioned above the burnpot bottom. The feed system supplies fuel initially to the burnpot bottom where it is ignited. After the initial ignition, the fire is continued by applying fuel directly to the slide where it is ignited, and after the cylinder has been rotated, the burning fuel is dropped onto the newly presented section of the cylinder or the slidable bottom. In one version of the embodiment, the hinges on the side of the cylinder may be expandable to permit the cylinder to rotate with substantial build up of ash on its surface.

In operation, a fire in the heating apparatus burns and builds up an accumulation of products of combustion to a higher and higher level. The burning coals are thereby raised from the rotatable cylinder to a level near a retention slide or above the level of the retention slide. If the burning coals are above the level of the retention slide, the slide can be moved into the coals so as to preserve a fire above them. If the burning coals are below but near the retention slide, fuel can be deposited on the slide and ignited by the fire below it. In either case, the cylinder is rotated or the burnpot bottom moved by sliding the coals on the rotatable or sliding surface removed to remove the ashes and/or clinkers. The burning coals from the slide are dropped on the newly presented section of the cylinder or on the slidable bottom. The furnace can operate for a limited time without a retention slide but may need to be ignited from time to time.

Instead of rotating about a horizontal axis, the ash removing section may rotate about a vertical axis. In this embodiment, there are two or more sections with one section closing the bottom of the burner and the other section permitting ash to drop from the burnpot. In the latter embodiment, the burnpot is shaped with the largest portion at the bottom to permit clinkers to fall from the burnpot freely. This may be combined with a similarly rotating retention slide so that the burning fuel is maintained on the retention slide while the ash removing system has an opening bottom section in position to permit ash and clinkers to fall out of the burnpot and rotated to an open position when the ash removing section is closed to receive the burning coals. If corn or other hard to ignite biomass is the fuel, the automatic ignition system with a hopper containing easily ignited fuel such as wood and a second hopper containing the harder to ignite biomass as described above may be used.

From the above description, it can be understood that the burnpot of the invention and stoves that accommodate it have several advantages, such as: (1) a continuous flame may be maintained while byproducts of burning are automatically removed; (2) difficult to ignite fuels may be ignited automatically; and (3) biomass such as corn that, when burnt, has a tendency to cause ash to stick to the burnpot may be utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

The above noted and other features of the invention will be better understood from the following detailed description when considered with respect to the following drawings in which:

FIG. 1 is a perspective view of an embodiment of the invention;

FIG. 2 is a fragmentary perspective view of a furnace that is another embodiment of the invention;

FIG. 3 is simplified fragmentary side view of the stove of FIG. 1 in accordance with an embodiment of the invention;

FIG. 4 is a simplified fragmentary side view of the embodiment of heater of FIG. 2;

FIG. 5 is an exploded perspective side view of an embodiment of burnpot in accordance with an embodiment of the invention;

FIG. 6 is another exploded perspective view of the embodiment of FIG. 5;

FIG. 7 is an enlarged fragmentary perspective view of a drum used in the embodiment of FIGS. 2 and 4-6;

FIG. 8 is a simplified perspective view of the embodiment of FIGS. 2 and 4-7;

FIG. 9 is a bottom view of the embodiments of FIGS. 2 and 4-8;

FIG. 10 is another simplified fragmentary side view of the stove of FIG. 1 in accordance with an embodiment of the invention;

FIG. 11 is a plan view of a burnpot in accordance with an embodiment of the invention;

FIG. 12 is an elevational front view of the embodiment of FIG. 11;

FIG. 13 is an elevational side view of the embodiment of FIG. 11;

FIG. 14 is a simplified side view of a firebox useful in the embodiment of FIG. 1;

FIG. 15 is a plan view of an openable bottom of the burnpot of FIGS. 3 and 10-14 in accordance with an embodiment of the invention;

FIG. 16 is a side view of the openable bottom of FIG. 15 in accordance with an embodiment of the invention;

FIG. 17 is an elevational front view of the openable bottom of FIG. 15 in accordance with an embodiment of the invention;

FIG. 18 is a fragmentary exploded perspective view of the embodiment of FIGS. 2 and 4-9;

FIG. 19 is another fragmentary perspective view of the embodiment of FIGS. 2, 4-9 and 18;

FIG. 20 is a sectional view of a fuel ignition system usable in the embodiment of FIGS. 2, 4-9, 18 and 19;

FIG. 21 is an exploded perspective view of the ignition system of FIG. 20;

FIG. 22 is a plan view of a combustion retention slide in accordance with an embodiment of the invention;

FIG. 23 is a front elevational view of the combustion retention slide in accordance with the embodiment of FIG. 21;

FIG. 24 is a side view of the combustion retention slide of FIG. 22 in accordance with an embodiment of the invention;

FIG. 25 is a side view of a heat exchanger tube scraper in accordance with an embodiment of the invention;

FIG. 26 is a plan view of the heat exchanger tube scraper of FIG. 25 in accordance with an embodiment of the invention;

FIG. 27 is a block flow diagram illustrating the steps used in cycling a corn stove in accordance with an embodiment of the invention;

FIG. 28 is a block flow diagram illustrating the steps used in cycling a corn stove in accordance with an embodiment of the invention;

FIG. 29 is a simplified block diagram of an ignition control system in accordance with an embodiment of the invention;

FIG. 30 is a block diagram of the process of igniting the stove of FIG. 1 in accordance with an embodiment of the invention, and

FIG. 31 is a flow diagram of a process of igniting a heater in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

In FIG. 1, there is shown a perspective view of a burner 10, which may be for example a stove or furnace, having an enclosure 14, with an access door 12, an ash pan 16, a rod 20, a rod 22, a heat exchanger tube scraper rod 24 and a fuel hopper lid 18. The access door 12 has a transparent window through which a firebox can be seen having within it a burnpot chamber, a burnpot, a feeder system, an exhaust system, a heat exchanger system and a combustible air intake system, none of which are shown in FIG. 1. The fuel hopper in the preferred embodiment includes the hinged fuel hopper lid 18 in the top of the enclosure 14 exposing an opening through which fuel, such as for example wood pellets or corn can be poured. To permit operation of the stove or furnace 10 from outside the enclosure 14, the rod 20 is connected to an openable bottom of a burnpot (not shown in FIG. 1), the rod 22 is connected to a combustion retention slide (not shown in FIG. 1), and the heat exchanger tube scraper rod 24 is connected to a heat-exchanger scraper (not shown in FIG. 1).

For convenience in operating the burner 10 from outside of the enclosure 14, the rods 20, 22, and 24 extend from the front of the enclosure 14 and may be used in one embodiment to manually actuate operations within the enclosure 14 by moving the rods. The openable burnpot bottom rod 20 permits the openable bottom of the burnpot to be opened to remove clinkers from the bottom of the burnpot. The combustion retention slide rod 22 permits a combustion retention slide to either: (1) be moved under the surface of the burning fuel; or (2) be moved to a location just above the burning fuel and close enough to cause burning fuel poured onto the combustion retention slide to be ignited. If the combustion retention slide is moved just below the burning fuel, it serves to hold the burning fuel in the burnpot while a clinker is being removed. If it is moved to a location just above the burning fuel and sufficiently close to the burning fuel so that new fuel can be ignited above the combustion retention slide, it retains the new fire until the clinker is removed. After the clinker is removed, the combustion retention slide can be removed from the opening in the burnpot to permit the burning fuel to drop to the bottom of the burnpot. This enables a fire to burn while the clinker is removed from the burnpot by opening the openable bottom of the burnpot (not shown in FIG. 1).

In FIG. 2, there is shown a simplified perspective view of a furnace 10B in accordance with an embodiment of the invention having a hopper system 274, an ignition system 276, a fuel drop chute 258 and a burnpot 26A. In this embodiment of heater, the hopper system 274 supplies fuel through the drop chute 258 to the burnpot 26A, where it is ignited by the ignition system 276. The burnpot includes a rotatable bottom and a two stage fuel supply system that starts a fire with an easy to ignite fuel and a fuel supply that feeds a harder to ignite fuel after a fire is started. A cold temperature can automatically cause supply of the easy to ignite fuel and a hotter temperature can initiate feed of a harder to ignite fuel. Additional feeding of the harder to ignite fuel can be initiated by a falling temperature above the ignition temperature but below the ignition temperature or by a timer.

In FIG. 3, there is shown a burner 10 such as a stove or furnace or incinerator having a burnpot 26, a burnpot seat 28, an ash pan 16, a combustible air system 48, a convection air system 54, and a fuel feed system 56. With this arrangement, combustible air flows through the burnpot 26 around tubes of heat exchangers and the heated gaseous byproducts of combustion and excess air flows out of exhaust tubing. At the same time, convection air flows through the inside of the tubes of the heat exchanger and into the area to be heated. Of course, the combustible air or gaseous byproducts of burning could flow through the tubes of the heat exchanger and convection air around the tubes.

The burnpot 26 rests on the burnpot seat 28 having an opening with a flange that supports the burnpot 26 while leaving room for clinkers to fall through the burnpot when its openable bottom is removed to drop clinkers into the ash pan 16. The burnpot 26 has an openable bottom 52, side wall portions with apertures 72, an open top 34 and a combustion retention slide 86 (combustion retention slide 86 not numbered in this FIG. 3; see FIGS. 22, 23 and 24). It is within a burnpot compartment 30 which confines the combustible air so that it flows into the burnpot 26 to support combustion and rises above it to flow to the heat exchanger tubes and from there out the exhaust tubing which may exhaust into the atmosphere outside of an enclosure containing the burner 10.

The combustion retention slide 86 (FIGS. 22 and 24) is positioned above the openable bottom 52 at a location where the fire burning from the openable bottom 52 upwardly will rise on the byproducts of burning to a level just beneath the location of the slide when it is moved into the burnpot. In this location, new fuel may be applied on top of the combustion retention slide 86. At this location, the fuel resting on top of the combustion retention slide is ignited by the fire beneath it. After this has happened, the openable bottom may be opened, such as by removing it from the bottom of the burnpot, to permit the byproducts of combustion to drop into the ash pan 16. In the alternative, if the byproducts of combustion lift the burning coals (typically corn or other biomass) above the location for the combustion retention slide 86, the slide may be forced just below the burning coals to support them. The openable bottom may then be removed so that the clinker drops downwardly. In both cases when the combustion retention slide is pulled outside of the burnpot or to one side, the burning combustion will drop to the bottom.

The burnpot 26 itself is shaped in the manner of an inverted truncated funnel with a smaller opening at the top and a larger openable bottom. There may be straight portions or other portions but the outward slanting walls must slant far enough outward between the top and the bottom so that the clinker will pull free against the resistance of the side walls. In this specification, we would define the shape of the burnpot as a generally truncated, inverted-funnel shape, with the understanding that this would encompass many geometries such as an inverted truncated cone or a truncated pyramid with a truncated top that is smaller than the operable bottom. To be operable, it is necessary for the clinker, which in the case of a corn burning stove is frequently one solid mass of byproducts of combustion, to drop out of the bottom rather than sticking to the sides as would be the case generally with vertical walls or funnel shaped walls with a smaller bottom than top. The combustible air system 48 in FIG. 3 includes the exhaust blower 78, a heat exchanger system 38 and outlet pipes 88 to permit exhaust to flow out of a housing for the stove and inhabitants into the outside atmosphere. The heat exchanger system 38 includes an upper heat exchanger 40 generally positioned horizontally and a back heat exchanger 44 generally positioned vertically.

With this arrangement, the combustible air follows a flow path from an inlet 80A in the direction of the arrows to 80B downwardly to 80C where it passes into the openable bottom 52 of the burnpot 26 and through the apertures 72 in the side wall portions of the burnpot 26 to support combustion therein and then upwardly as shown at 80D around heat exchanger top pipes 36 of the upper heat exchanger 40 as shown at 80E and 80F and from there downwardly as shown at 80G through the back heat exchanger 44 and to the exhaust blower 78 following the path shown at 80H and 801 to the exhaust pipes 80J, 80K, and 80L for exiting into the atmosphere through the exhaust outlet pipes shown schematically at 88. Similarly, the convection air system 54 includes a convection air blower 90 which draws convection air through a flow path including an air inlet shown by the arrow 92A through tubing following the path shown at 92B upwardly around back heat exchanger 44 as shown at 92C upwardly through the upper heat exchanger 40 as shown at 92D, 92E, 92F, 92G and 92H into the space that is to be heated by the stove 10.

Because the byproducts of combustion accumulate on the heat exchanger top pipes or tubes 36, a heat exchanger tube scraper 94 (not shown in FIG. 3) is mounted to be moved across the heat exchanger tubes 36 when the heat exchanger tube scraper rod 24 (FIGS. 1 and 2) is moved from outside of the stove enclosure 14. In this manner, the heat exchanger tubes 36 can be kept relatively clean and the space between them sufficiently clear to permit efficient heat exchange to the convection air through the inside of the tubes.

In FIG. 4, there is shown a side elevational view of an embodiment of heater 10B similar to the embodiment of FIG. 3 and having similar reference numerals for similar parts. However, the embodiment of FIG. 4 is intended to be used as a furnace and includes a movable bottom to the burnpot 26A in the form of a rotatable cylinder 268 positioned to rotate about axle 272 and serving as part of an ash removing section. The burnpot bottom opening is closed with a portion of the circumference of the rotatable cylinder 268 of the burnpot 26A.

In FIG. 5, there is shown an exploded perspective view of the burnpot 26A having a rotatable cylinder 268, flange members 62A, 62B, 62C and 62D (62D not being clearly shown in FIG. 5). Each of the flange members 62A and 62C have corresponding ones of the downwardly and outwardly slanting portions 110A and 110C and vertical portions 112A and 112C. The flange 62B extends straight outwardly and the flange 62D is reduced in size and shaped so that it may be positioned against a flat dividing wall as shown in FIG. 3. The flange portions are shaped to intimately contact the inside walls of the burnpot compartment and seal it to maintain combustible air underneath the flange assembly and the exhaust system that includes the open top 34 of the burnpot 26A.

The flange assembly includes an opening housed by the rotary perforated drum 268. The rotary drum 268 includes a plurality of divider walls 322, which in the preferred embodiment are formed of a plurality of pins extending axially from the surface 318 of the drum 268 to form two sides of a compartment. In another embodiment shown in FIG. 5, the dividing walls are solid. Cylindrical radial portions 316A and 316B form the axial ends of the compartments to divide the drum into a plurality of sections bounded by the perforated surface 318 of the drum 268, the divider walls such as 322 and the side members 316A and 316B. An axle 272 passes through a central opening 356 in the side members 354 (only one being shown in FIG. 5) and the aligned openings 358 in the drum 268. Flanges 294, side members 300 and hooks 296 are movably positioned on each side of the drum 268 in the embodiment of FIG. 5 so that they may be moved outwardly for clinkers to pass between them and find ashes to pass through perforations on them but otherwise form sides for the drum as it rotates. In another embodiment (FIGS. 6 and 7) clinker breaking cutting members depend from the ash retainer 312 as is shown in FIG. 6. Pot scraper rods 306 are spring biased by ash retainer springs 304 to scrape products of combustion from the drum. An ash scraper 270 is spring biased against the drum 268 by a spring 310 to further scrape the surface 318 of the drum 268 and remove the products of combustion near the bottom of the drum.

In FIG. 6, there is shown another exploded perspective view of the burnpot 26A, ash retainer clips 302A and 302B that receive pot scraping rods 306 on each side to support it as well as an ash retainer 312. A plurality of cutters 356 are mounted parallel to each other and to the ash retainer 312 and exert a slicing force against clinkers to break up the clinkers as they drop from the bottom of the burnpot 26A.

In FIG. 7, there is shown a perspective view of a rotary drum 268A, illustrating dividing walls 322A formed of pins 320. There are a plurality of such walls, and in FIG. 7, the drum 268A has four such walls dividing the drum 268A into four sections bounded by the burnpot cylindrical side rims 316A and 316B, the surface 318A of the drum 268A and the divider walls 322A. In the embodiment of drum 268A, the surface 318A is not perforated throughout but is smooth. This is an optional embodiment which may be utilized to provide a smooth surface for the removal of ash. It also will reduce the rate of burning by reducing the flow of air, and in that manner, reduce the heat when biomass such as corn is being burned. A reduction of the heat of combustion acts to reduce the sticking of clinkers to the surfaces of the burnpot.

In FIG. 8, there is shown a perspective view of the burnpot 26A illustrating the manner in which the ash retainer clip 302A is mounted to the pot scraper rods 306 on each side of the drum so that as the drum rotates, the rods 306 pull the ash retainer clips 302A and 302B (FIG. 6) so that the rods 306 move over the pin divider walls 322A (FIG. 7) and scrape the drum surface 318A (FIG. 7) and the wall surfaces.

In FIG. 9, there is shown a bottom view of the burnpot 26A showing the clinker cutters 324 mounted to the ash retainer 312 to break up clinkers rotating between them and the drum. These cutters are parallel to each other and spaced to move between the divider pins 320 forming the divider walls to break up clinkers for easier removal. An embodiment with solid divider walls may be preferred for finely divided biomass fuels such as wheat to avoid falling between pins or other openings but a divider with openings for clinker breaking disks may be preferred for biomass such as corn that forms larger clinkers.

As best shown in FIGS. 5, 6 and 8, two side members or fillers 300A and 300B (only 300B shown) are mounted next to the cylinder 268A. Hinged ash retaining springs 314A and 314B (FIG. 5, only 314B shown) may move outwardly to permit large clinkers or the like to drop out. The side members 300A and 300B have respective spring hooks 296A and 296B (only spring hook 296B being shown in FIG. 5) mounted to them to receive springs 304A and 304B (only 304B being shown in FIG. 5) biasing them closed. A scraper 270 is mounted to remove products of combustion that may adhere to the cylinder 268A. The springs 298A and 298B are positioned to hold the ash retainers 312 in place until the cylinder 268A is positioned to release the ash but to permit large solid clinkers to be carried by the cylinder and dropped outside of the burnpot.

In FIG. 4, there is shown an enlarged view of the burnpot 26A positioned with respect to the chute 258 and ignition system 276 (FIG. 18). In FIG. 8, there is shown a simplified perspective view showing the cylinder 268 with a perforated surface that permits air to enter the sides and exit upwardly into the bottom of the burnpot 26A to support combustion on its surface. In FIGS. 5 and 6, there are shown a perspective view and an exploded perspective view of the embodiment of burnpot 26A shown in FIG. 4 having hinges 294A and 294B (FIGS. 5 and 6), spring hooks 296A and 296 B (296B not shown in FIG. 6), open top 34, rotary perforated cylinder 268A and scraper 270. In FIG. 5, the scraper 270 and scraper spring 310 are shown in greater detail. It is positioned with respect to the cylinder 268A at a location removed from the burnpot bottom opening and extends along the lateral length of the cylinder 268 to scrape solid byproducts of combustion from the cylinder 268A.

In FIG. 10, there is shown a simplified sectional fragmentary view of the fuel feed system 56 for the embodiment of FIG. 3 within the burner 10 having a fuel hopper lid 18, a fuel hopper 32, an auger system 98, a fuel guide 102, drop tube 100. With this arrangement, fuel hopper 32 is dropped to the auger system 98 which moves it upwardly into the drop tube 100. From the drop tube 100 it falls to the fuel guide 102 which guides it to the opening top 34 of the burnpot 26. The fuel hopper 32 is sized in accordance with the speed of the auger 98 so as to move fuel into the drop tube 100 for application by the guide 102 to the burnpot at a rate for efficient burning at different heat settings to avoid blocking of air to the burning coals. The amount of fuel in the fuel hopper and the feed rate may be preselected for fixed periods of time such as 24 hours so that the ash pan can be emptied, the ash dropped down from the burnpot by pulling the openable bottom and fuel added at each convenient period, which may be 24 hours or perhaps twice a day, once late at night and again early in the morning as preselected by the user.

While a stove particularly adapted for the burning of biomass is illustrated in FIGS. 1-4 and 10, any combustion device may utilize the novel burnpot of this invention. Moreover, while a specific fuel feeding system is described, there are many such variations in feed systems, any of which can be employed with the proper combustion system. In the specific system of FIGS. 1-4 and 10, the bottom of the burnpot is openable. In the preferred embodiment, it may slide completely free of the burnpot so that a large clinker or fused mass of already burnt coals may be dropped through the bottom. The burnpot is shaped to expedite this process. However, the openable bottom may take on different configurations. It may be slide mounted within a bottom panel or it may be hinged to open and drop down or it may be one that is held in place by detents which can be removed to permit the dropping down of the bottom into the ash pan. Any of these configurations are workable.

The openable bottom performs two functions. One of the functions is to hold the ash until it is desirable to move the ash while still maintaining combustion above the ash. The other function is to permit an air passageway through the bottom. Preferably, a double walled openable bottom is used in which the top side of the double wall has perforations so that air may flow into the double box through perforations such as on the side or through the top portion that doesn't sit entirely below the burnpot but is within the burnpot wrap and upward through perforations in the top wall. Pulling the box out entirely opens a passageway to the bottom, but when the box is in place, the solid bottom blocks the combustion air from flowing into the fire box. This function could also be performed by two separately removable plates with the bottom plate sealing the burnpot compartment and the top plate providing perforations beneath the combustion to permit the combustible air to enter the burnpot.

The burnpot is shaped to facilitate the dropping of the clinkers when the slide is removed. In the preferred embodiment, that shape has a tapered side wall tapering inwardly at higher elevations to have a larger bottom than top. This permits the ready dropping of the clinker. Straight walls at times impede the dropping of the clinker as do funnel shaped walls so that the bottom is smaller than the top.

The side walls of the fire plate are shaped so that the weight of the clinker is sufficient to create a force that overcomes the frictional attachment to the sides of the burnpot. In the preferred embodiment, the walls slant outwardly in a manner of an inverted truncated funnel. The walls can actually form any configuration such as a slanting parallelopiped as well as a funnel shape or it can be pyramid shaped or any other configuration that permits a relatively easy pulling of ash free from the walls to permit it to drop into the burnpot. The walls must be shaped so that there is sufficient weight of the clinker that occurs because of the overall shape of the walls to pull the clinker past any portion of the wall to which it tends to stick. The stationary frictional force must be less than the weight of the ash that is dropped from the top surface of the removable ash to the bottom removable plate.

Although the bottom of the burnpot must be larger than the portions of the burnpot above the bottom that will contain the ash, it still must be sufficiently small to contain the combustion to an area that maintains heat sufficient for sustainable combustion. The top and bottom areas are defined by the need to obtain fuel through the top and at the bottom to be sufficiently close in size to maintain combustion. Preferably, the walls should slant outwardly at an angle of between 1 degree to 45 degrees from the normal. In the preferred embodiment, the walls are coned shaped and have an angle of six degrees.

In FIG. 11, there is shown a plan view of the burnpot 26 having the burnpot flange assembly 106, the open top 34 of the burnpot and the rear side 104 of the burnpot. The side 104 of the burnpot is positioned flat against one side of the burnpot compartment 30 (FIGS. 1 and 3) and the burnpot flange assembly 106 includes the flanges 62A-62C, the upwardly extending wall portions 123, 124 and 126 and the angled portion 122. The flanges 62A-62C are positioned on the other sides to seal the burnpot compartment 30 with the combustible air system being beneath the burnpot flange assembly 106 and the exhaust system being above the burnpot flange assembly 106 so that the open top 34 of the burnpot 26 that receives fuel and through which byproducts of combustion float is within the exhaust system and are insulated from the combustible air system. The walls 123, 124 and 126 extend upwardly to prevent corn from bouncing out of the burnpot when moving downwardly from the feed chute 258 that fits against the angled portion 122. A screw can be positioned in the feed chute 258 to scatter the corn and reduce bounce.

In FIG. 12, there is shown a front view of the burnpot 26 illustrating the flange assembly 106 and the combustible air portion 118. The burnpot flange assembly 106 includes the side flange members 62A and 62C having corresponding ones of the downwardly and outwardly slanting portions 110A and 110C and the vertical portions 112A and 112C. These portions are shaped to intimately contact the inside walls of the burnpot compartment and seal it so as to maintain combustible air underneath the flange assembly 106 and the exhaust system including the open top 34 of the burnpot 26 above the burnpot flange assembly 106.

The flange assembly 106 includes the opening 116 formed as a regular parallelopiped in the preferred embodiment and having the flange assembly 106 at its bottom end. The flange assembly 106 includes the downwardly extending flanges 62A and 62C and a vertical outwardly extending flange 62B on the front that seals the combustible air section from the exhaust section by lying flat upon a horizontal portion of the burnpot compartment (not shown in FIG. 12). It separates the exhaust portion 116 of the burnpot from the combustible air portion 118 of the burnpot.

The combustible air portion 118 of the burnpot includes the perforated walls 108 of the burnpot that angle outwardly to permit easier dropping of the coals from the burnpot. The perforations 72 through this surface or surfaces are sized and angled so as to cause combustible air to flow downwardly into the flame. Near the top portion of the perforated section are a number of slots 120 to receive the combustion retention slide used as described above to sustain combustion while used coals from beneath it are being dropped. It is positioned at a level high enough to support the byproducts of combustion and the build up thereof for a convenient period of time, after which the combustion retention slide is moved over the top of the burnpot to sustain combustion while the coals underneath it are removed. Thus the feeding of fuel, the insertion of the combustion retention slide and the removal of burned ash from the ash pan underneath the fire box are all timed so as to be convenient for the user.

In FIG. 13, there is shown a side view of the burnpot 26 illustrating the manner in which the flange 62C extends outwardly and then slopes downwardly into the flanges 62A and 62B to form a compartment into which air may be injected for passage through the openings 72 and use in burning of the fuel.

Generally, in the preferred embodiment, the diameter of the apertures are 1/16 to ⅜ inch, and they are spaced so that, as the byproducts of combustion increase and lift the burning coals and block holes, sufficient air is provided in the burnpot to maintain a rate of burning that avoids excessive fusing of the fuel to each other. The holes are spaced a minimum of 0.375 inch apart and a maximum of 1.5 inches apart. The fusing of the corn can cause suffocation of the fire and reduced heat. They are drilled so that the internal walls slant downwardly to a level at which a combustible fire is at some times burning. They point generally downwardly into the location of combustion.

The openings 72 are angled and selected as to size to provide an adequate flow of air to the burning coals. A range of holes between 0.0625 inches in diameter and 0.375 inches in diameter have been found to be suitable. In the preferred embodiment they are spaced in 5 rows approximately 0.4 of an inch apart in the horizontal direction and approximately 6 inches apart in the vertical direction with a top row that is closer together. The lower rows are generally equally spaced in the preferred embodiment in four rows.

While round holes have been selected for convenience in the preferred embodiment the holes may be of any shape. The exact size, spacing, number of holes and shape are selected for maximum effect in sustaining an adequate level of combustion.

In FIG. 14 there is shown a fragmentary simplified side elevational view of the fire box 128 including the bottom portion of the burnpot compartment 30 with the burnpot seat 28 within it and at its upper end the heat exchangers 38. As shown in this view, the burnpot is mounted within the fire box 128 in a burnpot seat which adapts to the openable bottom 52 of the burnpot to permit the byproducts of combustion to drop down into the ash pan. At the top of the fire box 128 is the heat exchanger 38 which receives the exhaust from the burnpot for the purpose of generating heat while the combustible air is contained within the burnpot compartment 30. The burnpot compartment 30 is formed of the burnpot flange assembly 106 resting on top of the burnpot seat 28 to form a compartment which receives combustible air and permits exhaust to pass through the compartment from the burnpot. The side 122 is position against the back of the firebox and slots 129 are provided in the backplate to permit air to enter the burnpot compartment 30.

In FIG. 15, there is shown a top view of the openable burnpot bottom 52 having a perforated top surface 60, a bottom plate 74 with openable burnpot bottom wings 62A and 62B on each side and an upwardly extending flange 64. The perforated top surface 60 contains a number of regularly spaced combustible air apertures two of which are indicated generally at 66 of sufficient size to permit the combustible air to support a starting combustible bed. The burnpot (not shown in FIG. 15) sits above the openings 66 in the perforated top surface 60 and does not overlay the wings 62A and 62B nor the two elongated openings 68A and 68B in the perforated pot. The openings 68A and 68B are intended to permit combustible air to pass to the bottom surface of the perforated plate and then upwardly to the burnpot, with the plate 74 preventing escape from the burnpot chamber. An internally threaded nut 76 extends from the upwardly extending flange 64 to receive the rod 20 (FIG. 1). Openings may also be present in the right, rear and left sides 70A, 70B and 70C of the openable bottom.

In FIG. 16, there is shown a side view of the openable burnpot bottom 52 showing the top perforated surface 60, the upwardly extending flange 64 with the nut 76 welded thereto. As shown in this view, the flange 64 extends downwardly to a solid plate 74. In this arrangement, combustible air enters the openings 68A (FIG. 15) and 68B of the openable burnpot bottom 52 passes upwardly through the apertures 68A and 68B (68A being shown in FIG. 15). Although circular perforations perpendicularly thereto with the lip 136 extending from the top edge of the lip 134 and having within it the opening 138 for connecting to a pull rod 22. With this arrangement, the combustion retention rod may slide into the burnpot 26 (not shown in FIGS. 22-24) so as to preserve combustion while the byproducts of combustion or the coal beneath it are dropped through the bottom into the ash pan and then removed so as to drop burning coals down to the top surface of the replaced openable bottom of the burnpot so that it is unnecessary to continually reignite the fire within the burnpot. The combustion retention slide may take many different forms that provide a support for fuel near the burning coals beneath it such as a shutter format or partial movable plate or the like. It is only necessary to hold burning coals while the clinker is removed from the burnpot and drop them after the clinker is removed.

In FIGS. 25 and 26, there is shown a sectional side view and a plan view respectively of the heat exchanger tube scraper 94 having a base 140, a parallelopiped shaped edge 142 extending outwardly orthogonal to the flat base 140 so as to form a parallelopiped with a rectangular shape, an opening 146 in the edge 142 to receive a nut 148 welded thereto and a plurality of openings 150, each of which corresponds in diameter and location to a different one of the heat exchanger tubes. The nut 148 receives a pull rod which may be utilized to move the base 140 back and forth over the matching heat exchanger tubes and scrape deposits therefrom.

In FIG. 27, there is shown a block diagram 158 of the normal operation of the burner 10 having a subroutine 160 for igniting the burner and supplying fuel thereto and a subprocess 162 for removing the spent coals therefrom while continuing the burning. By continuing the burning, it is meant that it is unnecessary to extinguish the fire, clean the burner and restart the fire. The step 164 continues so that this process may be repeated for very long periods of time. The subprocess 160 are shown generally at 66 (FIG. 15) and two elongated slots at 68A and 68B, any openings that permit the flow of combustible air to the bottom of the burnpot will serve the appropriate function. Similarly, one slot or a multiplicity of slots could be used instead of the apertures 68A and 68B. Any arrangement that permits the flow of air is suitable.

To seal the bottom of the burnpot compartment, the wings 62A and 62B (FIGS. 15 and 17) are shown at the bottom of the double walled openable burnpot bottom but, of course, could be positioned elsewhere since their function is merely to support the double walled bottom and seal to sides or the burnpot openable bottom against the escape of combustible air when the openable bottom is in place closing the bottom of the burnpot. One of the other four sides is sealed against the flange 64 and the other is sealed against a wall of the burnpot chamber with slots to allow combustible air to enter the space between the perforated top and the bottom of the openable bottom. Similarly, as mentioned earlier, the perforated top portion 60 could be a separate sheet metal with perforations and the bottom portion 74 still another arrangement with each of them to be removed separately when the ash is to be dropped down. The top perforated surface 60 can be fastened to the bottom plate 74 by any suitable means such as welding or attachment. In the preferred embodiment, it includes downwardly extending tabs that fit within openings in the bottom plate 74.

In FIG. 17, there is shown a rear elevational view of the openable burnpot bottom 52 showing the upwardly extending flange 64, the nut 76, the top perforated plate 60 and the bottom plate 74 with the wings 62A and 62B. As shown in this view, the openable burnpot bottom may be moved into position by the upwardly extending member 64 by grabbing the rod 16.

In FIG. 18, there is shown an exploded perspective view of the embodiment of furnace or stove of FIGS. 2 and 4-9 having a burnpot 26A, a first fuel hopper 250, a second fuel hopper 252, a drive coupling 340 and an ignition system 276 closed in a cabinet 278A. As shown in this view, the cabinet 278A includes the hopper system 274, an opening 280 into a firebox, an air intake damper 282, a rotation gear motor cover 284, another revolution back panel 334 with an auger access panel for the hoppers at 332, an ash pan door 326, a blower access panel 286 and an exhaust fan panel 288. A filter for the furnace may be positioned as shown at 336 to be underneath the revolution back panel 334 with an opening in it to be aligned with the filter 336. As shown in this view, the burnpot 26A fits within the panel 278A within the opening in the housing above an ash pan 16A and behind a door 12A. A cover 338 is provided for the ignitor 276 to ignite the fuel within the burnpot. The rotary drive coupling 340 rotates the bottom of the burnpot to permit ash to drop into the ash pan 16A for removal.

FIG. 19 shows another exploded view of the embodiment of furnace 10B having the burnpot 26A, the ignition 276, the rotation drive shaft 342, the rotation motor mounting bracket 344 and the rotation motor switch 346 so that a rotation motor 348 may be turned on and off manually or programmed for automatic operation to rotate the drum in the firebox and remove ash. The combustion air exhaust blower 78 supplies oxygen and removes exhaust from the furnace and a convection air blower supplies convection air for heating of a room or the like as explained above in connection with the embodiment of stove 10. A hot air box 350 is heated and supplies hot air to heat transfer tubes.

In FIG. 20, there is shown a fragmentary elevational view, broken away, to show first and second fuel hoppers 250 and 252 respectively with corresponding first and second fuel augers 254 and 256 respectively mounted so that the first and second fuel augers move fuel from the first and second hoppers 250 and 252 respectively into the fuel chute 258 (FIG. 4). The first and second fuel augers 254 and 256 are controlled by a control system to feed fuel into the burnpot 26A through the feed chute 258 as needed. In one embodiment, an easy to ignite fuel is moved into the burnpot 26A from the first fuel hopper 250 by the first fuel auger 254 for ignition by an ignition system and when the temperature of the burnpot is sufficiently high a harder to ignite fuel is moved into the burnpot 26A from the second fuel hopper 252 by the second auger 256. Similarly, FIG. 21 is an exploded, fragmentary perspective view of the first and second fuel hoppers 250 and 252 and first and second fuel augers 254 and 256. The first and second fuel hoppers 250 and 252 have bottom surfaces that slant downwardly with the augers 254 and 256 being located at the lowest points 260 and 262 respectively in the hoppers as best shown in FIG. 19. In FIG. 20, there is shown a sectional view of the second hopper 252 with the second auger 256 positioned to receive fuel from any of the sides. The starting of the augers may be by manually closing a switch or by a heat sensor. A heat sensor may cause easy to ignite fuel to be deposited in the burnpot and a higher temperature may cause harder to ignite fuel to be deposited. In some embodiments, this arrangement may also be used to adjust the temperature of the burnpot by automatically changing the proportions between a higher heat of combustion fuel and a lower heat of combustion fuel in response to temperature changes during operation of the stove or furnace.

In FIGS. 22, 23 and 24, there is shown a plan view, a front elevational view, and a side elevational view respectively of a combustion retention slide 86 having eight fingers 130A-130G of a combustion retention slide 86, a bottom retention plate 132, an upwardly extending edge 134, an upwardly extending lip 136 and a nut hole for the combustion retention slide rod 22. The fingers 130A-130G are formed in the bottom retention plate 132. The upwardly extending edge 134 is integrally formed with the bottom plate 132, and in the preferred embodiment, extends for igniting the fire and supplying fuel to it, includes the steps 166 of closing the openable bottom or insuring that it is closed, the step 168 of igniting the fuel on top of the openable bottom and the step 170 of feeding fuel to the fire as needed.

The subprocess 162 includes the steps 172 of pushing the combustion retention slide either under the coal bed that has reached its level on top of spent coals or pushing it just above the coals so that it is close enough to ignite new fuel, the step 174 of forcing the openable bottom sufficiently Jar open while the coals are still burning to permit removal of the spent coals while the burning continues above the combustion retention slide, the step 176 of moving the openable bottom under the burnpot again to close the bottom and the step 178 of moving the combustion retention slide from blocking the burnpot to let burning coals drop to the top of the openable bottom.

In FIG. 28, there is shown a flow diagram of a process 238 of building a fire in a furnace to burn difficult to ignite fuel using the embodiments of FIGS. 18-20 having the step 240 of igniting fuel on burnpot movable bottom, the step 242 of sliding the retention slide under the burning coals or just above the burning coals and adding fuel to the retention slide, the step 244 of rotating the movable bottom to remove the products of combustion from the burnpot, the step 246 of moving the combustion retention slide from blocking the burnpot to let the burning coals drop to the burnpot moveable bottom, and the step 248 of repeating steps 242 to 246 as often as necessary to kept the fire burning.

In FIG. 29, there is shown a block diagram 180 of a stove ignition system including a printed circuit and microcontroller 182 or other control arrangement, a fuel feed and air control system shown generally at 186, and an igniter shown generally at 188. The printed circuit and control 182 may include a timer and drivers 131 and 133 or a microprocessor or any other suitable arrangement. The controller 182 communicates electrically with the thermostat 184 so as to maintain an even temperature in the warmed place, with the fuel feed and air circulation system 186 and with the igniter 188. With this arrangement, the cycle of feeding fuel, removing ash, providing combustible air and removing exhaust are controlled. The fuel feed and air control system 186 includes a proof of fire detector 190, an air switch 192, a gear motor drive and auger combination 194, a combustion blower 196, a convection blower 198 and a manual temperature switch 200. Each of these units communicates with the control system 182 to determine when air is to be supplied for combustion, when fuel is to be ignited and the like.

In FIG. 30, there is shown a block diagram 202 illustrating the routine controlled by the control system of FIG. 29 for ignition of a fire in the burner 10 having a startup system 204 and a level by level flow rate system 206. The startup system 204 includes the steps 208 of pushing the power button for combustion air fan and for the convection air fan, the step 210 of providing a thirty second delay, the step 212 of turning off the convection fan and moving the combustion fan to setting 1, which is the lowest setting, the step 213 of starting the feeding of fuel at level 1, and the step 214 of waiting to sense the proof of fire switch. With this arrangement, ignition is tried and then the fuel ignited with the fans going. There is a thirty second delay and then the convection fan goes off since there is no heat being provided yet and the combustion fan provides a very low flow of combustion for startup. The final step in this sub-routine is waiting for the proof of fire switch to close.

The subprocess 206 includes the step 216 of sensing proof of fire. There may be a series of five minute delays. If fire is detected, the fans and auger are moved to level 2 for five minutes, but if it is not detected then the cycle must start again with pushing the power button. At step 218, which is level 2, the combustion fan and feed rate increase for five minutes and then goes to step 220 which is level 3 providing a stronger flow of combustion air and more fuel for five minutes and then to step 222 which is level 4 providing a still higher rate of combustion air and another increase in fuel for another five minutes and then step 224 which is level 5 for five more minutes. This is the maximum setting for combustion fan and fuel feed setting, the air flow and fuel feed may also be controlled by a thermostat to maintain the temperature in the space being heated constant. This example shows the sequence of the control board to the maximum level (level 5). During normal operation, the sequence stops at any of the five levels that can be chosen as the desired level of operation.

In FIG. 31, there is shown a flow diagram 226 of a process of igniting the heater in the embodiment of FIGS. 18 and 19 including the step 228 of igniting the easy to ignite fuel using the start up process 204 of FIG. 29, the step 230 of sensing proof of fire, the step 232 of stepping to the appropriate level of convection and feed to build a fire hot enough to ignite a harder to ignite fuel in the second hopper, the step 234 of terminating the feed of the easy to ignite fuel from the first hopper and starting the feed of the hard to ignite fuel from the second hopper and the step 236 of stepping the level of convection and feed to the desired heating of the furnace.

Although a preferred embodiment of the invention has been described in some detail, many modifications and variations of the invention, within the scope of the appended claims, may be utilized without deviating from the invention. Accordingly, the invention may be performed other than has been specifically described utilizing the known equivalents in the art as illustrated in the files of the United States Patent and Trademark Office and in the technical literature, without deviating from the invention. 

1. A burnpot having a burnpot bottom opening closed by a movable bottom; said moveable bottom comprising; a rotatable member having a horizontal axis of revolution; said rotatable member having a portion closing said burnpot bottom; whereby products of combustion are temporarily supported by a surface of the rotatable member to enable a body of combustible fuel to burn on its upper surface; a mounting structure positioned with respect to the rotatable member so that its surface always closes the burnpot at the bottom end of the burnpot and extends sufficiently beyond an opening at the lower end of the burnpot to carry the products of combustion out of the burnpot when the rotatable member is rotated.
 2. A burnpot in accordance with claim 1 wherein a rotatable bottom is cylindrical and has a radius of curvature sufficiently large to provide a bottom to the burnpot that avoids excessive collection of combustible fuel at the outer edges of the burnpot bottom.
 3. A burnpot in accordance with claim 2 wherein the radius of curvature of the rotatable bottom is sufficiently large with respect to the size of the burnpot bottom opening so that the distance between a lowest point on the burnpot bottom is no more than 24 inches from a highest point.
 4. A burnpot in accordance with claim 1 in which the burnpot includes side wall portions and a top portion; the burnpot side wall portions and the top portion of said burnpot being shaped to permit a solid clinker to move out of the burnpot bottom opening by rotation of the rotatable member.
 5. A burnpot in accordance with claim 1 wherein a combustion volume is provided between said burnpot bottom opening, side wall portions and a top; said combustion volume having an upper portion and a lower portion whereby a fire on a combustion surface in said lower portion burns upwardly toward said upper portion so that byproducts of combustion build on the combustion surface to cause burning fuel to burn at a higher level; said higher level having a smaller cross sectional area than said lower portion whereby the byproducts of combustion may drop as a unit out of said burnpot bottom opening.
 6. A burnpot in accordance with claim 1 in which burnpot side wall portions include apertures through them having internal walls, each of said apertures having a corresponding diameter and internal wall thickness; said thickness being equal to the thickness of the side wall portions; said side wall portions slanting downwardly toward an openable bottom whereby air entering the side wall portions flows with velocity in the direction of said openable bottom.
 7. A burnpot in accordance with claim 1 further including a control system having means for moving from a fuel feed setting to a fuel feed setting in a controlled serial sequence.
 8. A burnpot in accordance with claim 7 further including a delay time between the fuel feed settings to avoid a rapid change in rates of fuel feed.
 9. A burnpot in accordance with claim 1 further including at least one scraper positioned to scrape at least one of products of combustion and fuel from the rotatable member as it rotates.
 10. A burnpot in accordance with claim 1 further including fragmenting members for fragmenting clinkers as the rotating member rotates.
 11. A method of operating a heating apparatus comprising the steps of: permitting fire in the heating apparatus to burn and build up an accumulation of products of combustion; maintaining burning coals on an upper surface of a rotatable member; and rotating the rotatable member when the coals have built to a predetermined level, whereby the coals are removed.
 12. A method in accordance with claim 11 further including the step of scrapping products of combustion from the rotatable member.
 13. A method in accordance with claim 11 wherein the step of rotating the rotatable member includes the substeps of rotating a cylinder while the coals are still burning and rotating the cylinder after fuel is at least substantially burnt.
 14. A method in accordance with claim 11 wherein a portion of fuel is burned at the top of the fuel before rotating the rotatable member whereby a burnpot is not overheated, the rotatable member is rotated to loosen the fuel before the burnpot is overheated and the rotatable member is rotated again to remove ash.
 15. A method in accordance with claim 11 further including the step of moving from a fuel feed setting to a fuel feed setting in a controlled serial sequence.
 16. A method in accordance with claim 15 further including a delay time between the fuel feed settings to avoid a rapid change in rates of fuel feed.
 17. A heating apparatus, including: a burnpot; a fuel feed system; said fuel feed system including at least first and second fuel hoppers and fuel moving apparatuses in contact with said at least first and second fuel hoppers; said fuel moving apparatuses being positioned to move fuel from either said first or said second fuel hoppers into the burnpot.
 18. A heating apparatus in accordance with claim 17 further including a control system and an ignition system; said control system comprising a switching system having at least a first state and a second state wherein said switching system energizes said fuel feed system to move fuel from said first fuel hopper into said burnpot and energizes said ignition system when in said first state and, when said switching system is in said second state energizes said fuel feed system to move fuel from said second fuel hopper into said burnpot.
 19. A heating apparatus in accordance with claim 18 wherein said switching system switches from said first state to said second state when the temperature in the burnpot reaches an ignition temperature of the fuel in said second fuel hopper.
 20. A method of igniting fuel in a burnpot comprising the steps of: feeding an easily ignitable fuel from a first hopper into a burnpot; igniting the easily ignitable fuel in the burnpot; and feeding a harder to ignite fuel to the burnpot when the temperature in the burnpot reaches an ignition temperature of the hard to ignite fuel. 